Efforts to determine the nature of the uterokinins which were associated with partially purified bombesin recovered from bovine milk, have led to purification of two of the kinins, one of which has been identified as bradykinin. This finding led to an examination of the present state of understanding of bradykinin in the central nervous system. Present proof that bradykinin occurs in the brain derives from evidence utilizing a combination of chromatographic, RIA and radioreceptor assays. The variability in quantitative estimates of bradykinin levels in various regions of the brain are presumed to reflect, in part, characteristics of antibodies used in RIAs. It appears that gonadal steroids modulate bradykinin-like immunoreactivity in the pituitary, however, there is disagreement as to the qualitative and localized nature of such modulation; this may indicate that multiple kinins are being recognized in the RIAs. It is anticipated that lessons learned in purification of milk uterokinins will be applied to determine the precise nature of the kinins which occur in brain tissues, e.g., hypothalamus and pituitary. Since arachidonate metabolites have been demonstrated to mediate bradykinin receptor interactions, a more precise definition of the qualitative nature of brain bradykinin(s) will complement other studies in this laboratory which implicate arachidonate metabolites in central mediation of gastric acid regulation by various opiate peptides and bombesin.